Allen Road, formally known as William R. Allen Road, is a short municipal expressway and arterial road in Toronto, Ontario, Canada. It starts as a controlled-access expressway at Eglinton Avenue West, heading north to just south of Transit Road, then continues as an arterial road north to Kennard Avenue, where it continues as Dufferin Street. Allen Road is named after Metro Toronto chairman William R. Allen and is maintained by the City of Toronto. Landmarks along the road include the Lawrence Heights housing project, Yorkdale Shopping Centre and Downsview Park, and Downsview Airport. A section of the Line 1 Yonge–University subway is located within the median of the expressway from Eglinton Avenue to north of Wilson Avenue.

The portion south of Transit Road was originally constructed as part of the Spadina Expressway project. The Spadina was proposed in the 1950s as a north–south freeway, intended to connect downtown Toronto to the suburbs of North York and to serve the Yorkdale Shopping Centre project; it was only partially built before being cancelled in 1971 due to public opposition. Initially proposed in the 1950s as part of a network of freeways surrounding Toronto, its cancellation in 1971 ended proposals for other proposed expressways into and around Metro Toronto. Despite this, extensions were opened south to Eglinton in 1976 and north to Kennard Avenue in 1982.

In 1983, the Province of Ontario, the City of Toronto and the government of Metropolitan Toronto (Metro) agreed to a land transfer that saw a strip of land south of Eglinton, as well as the right-of-way for the proposed expressway, transferred to the city in exchange for the fully-constructed arterial extension of Highway 400 now known as Black Creek Drive. Various proposals since to extend Allen Road south of Eglinton—either above or below ground—have never gained traction, and the route remains a backlogged stub of the original proposals. Despite this, the decision to cancel the Spadina—and by extension similar expressways into downtowns—has been regarded as one of the defining moments of urban planning in Canada.

Allen Road is a 7.3-kilometre (4.5 mi) road located within Toronto. The four-to-eight lane route connects Eglinton Avenue West with Kennard Avenue, north of which the roadway continues as Dufferin Street. It is classified by the City of Toronto as an expressway from Eglinton Avenue to Transit Road and as a major arterial from Transit Road to Kennard Avenue. As such, bicycles and pedestrians are prohibited on the route south of Transit Road. The outermost lanes of Allen Road from Sheppard West station north to Kennard Avenue are high-occupancy vehicle lanes (HOV).

Allen Road begins at Eglinton Avenue West with two separate signalized intersections serving the opposing directions of travel on the expressway. The northbound lanes intersect Eglinton Avenue West to the east of Eglinton West station, while the two southbound lanes connect to Eglinton Avenue west of the station. It proceeds north to Lawrence Avenue West as a four-lane expressway with a speed limit of 80 km/h (50 mph) in the northerly direction until 500 m (1,600 ft) north of Eglinton Avenue.

The tracks of the Line 1 Yonge–University subway are situated between the carriageways in a 15-metre-wide (49 ft) right-of-way, with each station's TTC bus terminal also being located between them. The roadway intersects with Lawrence Avenue West, with the ramps to and from each carriageway meeting at a set of traffic lights. North of Lawrence Avenue, the route is eight lanes, with a speed limit of 80 km/h (50 mph). Ramps connect to and from Yorkdale Road, flanking Yorkdale station between them.

The Allen proceeds on bridges over the lanes of Highway 401, with ramps from the Allen to Highway 401 passing overhead. The interchange also serves to connect Yorkdale Road with Highway 401. The exit from the northbound Allen to Highway 401 serves as a ramp to both directions of Highway 401, with two lanes proceeding north of Highway 401. Similarly, two lanes are provided southbound over Highway 401, and access from the eastbound and westbound 401 merges with the Allen south of Yorkdale Road. Access to Yorkdale Road from the eastbound 401 is provided at the partial Dufferin Street interchange to the west. The southbound ramp from the Allen to the eastbound 401 flies over the whole interchange and connects with the eastbound 401 collector lanes. The subway is situated on bridges over Highway 401 between the northbound and southbound lanes.

North of Highway 401, the Allen is four or six lanes. It passes over Wilson Avenue, with Wilson station being above the namesake avenue within the median of Allen Road, and meets with Transit Road at a signalized intersection. The subway diverges from the route just north of Wilson Avenue, where there is a large subway yard and bus garage known as Wilson Yard, to the west of the road. Just south of Transit Road is a partial interchange with Wilson Heights, the former northern terminus of the road until 1982.